Project Summary Public health efforts in adolescence aimed at life course physical health promotion have to date focused almost exclusively on addressing physiological risk factors and health behaviors (e.g., weight, smoking, etc.). This proposal examines a far-reaching hypothesis with the potential to open up new venues for intervention: that social relationship qualities established in adolescence have an integral, long-term relationship to life course physical health and aging processes. The proposed study will clarify both the existence and the mechanisms by which two specific relationship qualities in adolescence?experience of hostile conflict and absence of supportive relationships?are linked to midlife health and aging outcomes. It uses uniquely rich longitudinal data on peer, romantic partner, and family relationship qualities across a 25-year span, to address four overarching aims: 1) direct prediction of midlife health & aging from adolescent social relationship qualities; 2) assessment of mediational vs. weathering explanations of links from adolescence to midlife health & aging outcomes; 3) examination of mediation of adolescent-midlife linkages via mental health and health behaviors; and 4) examination of biologic and contextual mediators and moderators of observed adolescent-midlife linkages. The proposed study addresses each of these Aims with a uniquely intense combination of repeated interviews, sociometric assessments, and direct observations of interactions with parents, peers, and romantic partners, with the new addition in midlife of an array of highly valid physiological indicators of health and aging?all obtained from a socio-demographically diverse final sample of 172 individuals (with 97% sample retention to date), followed across a 25-year span, from age 13 into midlife (ages 33 ? 37). The proposed study has significance in allowing: a. identification of several entirely new arenas within adolescence for potential interventions to promote lifelong health and healthy aging; b. suggest specific relational characteristics to target across this period in screening and preventive interventions; c. distinguish social processes in adolescence that directly predict accelerated aging (and are thus critical to address within adolescence) from those that lead to mediated chains of risk (which would suggest multiple promising points of intervention); and d. dramatically advance overall theoretical understanding of the ways in which early relationship difficulties are linked to and potentially affect physical health and aging outcomes well into midlife.